# Homework Help: HELP - force of wind/torque on a building

1. Nov 14, 2005

### HPVic03

A 50 story building is being planned. It is to be 200 m high with a base 40 m by 70 m. Its total mass will be about 1.8 107 kg and its weight therefore about 1.8 108 N. Suppose a 200 km/h wind exerts a force of 840 N/m2 over the 70 m wide face (Fig. 9-73). Calculate the torque about the potential pivot point, the rear edge of the building (where FE acts in Fig. 9-73), and determine whether the building will topple. Assume the total force of the wind acts at the midpoint of the building's face, and that the building is not anchored in bedrock. [Hint: FE in Fig. 9-73 represents the force that the Earth exerts on the building in the case where the building is just beginning to tip.]

the picture is at:

http://www.webassign.net/giancoli5/9_73.gif

I know you multiply 200 by 70 to get the area that the wind is acting on, then multiply that by 840 to get the Newtons of that, but where do u go from there??? please help

2. Nov 15, 2005

### brewnog

So you have worked out the force acting on the building...

The question tells you to assume that the force acts at the midpoint of the face the wind is acting on, so that will help you out.

Do you know about turning moments/torque? Have you thought of treating the building as a big block?

3. Nov 15, 2005

### Astronuc

Staff Emeritus
Treat the wieght (downward force) of the building at the center of mass, and the moment is from the back bottom corner to the CM.

Treat the wind as a distributed load (lateral force) on the windward side on the same moment arm of the CM.